Process for electric steel furnaces



June v10, 1924. 1,497,554

Y J, DIXON I PRQCEsS FOR EI/JECTRIC STEVEL FURNACES Filed ay 27, 1915 sfJ'oxeph L. 17mm JOSEPH LAWTON DIXON,

TES PATENT OFFICE.

OF DETROIT, MICHIGAN.

PROCESS FOR ELECTRIC STEEL FURNACES.

Application filed May 27,

-make and use the same.

Proposals have been made for melting and refining steel and other metalsin electric arc furnaces by means of a process in which the metal ismelted by means of a long are at relatively high voltage, and thesubsequent refining of the metal carried on while the heating iscontinued by means of a shorter are at lower voltage.

In the invention which 1 now disclose I carry out the process in animproved manner which avoids the disadvantages of the process as,carried out in previous disclosurw;

Previous disclosures have proposed that the shortening of the arc shallbe accom- 'plished by merely lowering the electrode thereby causing alarger flow of current,

which larger current excites a reactance, which in turn automaticallycauses a de-- crease in the voltage applied to the electrode. In thatcase the lowering of the voltage is accomplished at the expense of anundesirable lowering of the ower factor. Still further, the voltage atthe electrode has difl'erent values for relatively different values ofthe current. There is a serious disadvantage for the followin reasonsAlthough the power supply to the furnace during refining ls'in generalless than that during melting, yet the power requirements duringrefining are far from being constant, and in general great variationsare necessary during the refining of a single heat.

The necessary variation in the power supply must be obtained by raisingor lowering the electrode, which movements, respectively, cause adecrease and an increase in the current. The alteration in the currentis accompanied by a very large alteration ofthe voltage in the oppositedirection. Therefore any attempt to adjust the power supply by raisingorlowering the electrode is largely neutralized by the opposing variationsof the current and of the voltage. It

tween the metal and the electrode.

1916. Serial no. 100,177.

follows that a relatively small variation in the power supply can beaccomplished only by a relatively large lengthening or shortening of theare. As a result it is found impossible to conduct the refining andsatisfy the demands of each movement as regards power supply withouthaving an undesirably long are during part of the period of refining. Inthis way the objects of the process are to a large extent defeated.

In my invention I carry out the process in a manner such that thevoltage is substantially independent of the current How, and also suchthat the voltage may be lowered without lowering the power factor.

Toaccomplish this, I supply the electric powerto the furnace through atransformer, the windings of which'are so arranged that the ratiobetween the primary and secondary voltages may be varied independentlyof the electrical load taken from the transformer.

The drawing is a diagrammatic illustration of the apparatus I providefor carrying out my invention. I

in theodrawing, ais an electric furnace, b is an electrode which may beraised or lowered; c and c are conductors by which the electric power isconveyed to the furnace, d

a transformer having a primary and secondary winding (Z' and drespectively; e

and e are switches by meansof which theprimary windings of thetransformer is connected to the supply mains f and f leadingfrom thegenerating station, not shown. The two: switches e and e are connectedto the transformer in a manner so that'by closing 0 there are includedin the circuit a smaller number of turns of the primer winding than isthe case when R is'close Therefore, when switch e is closed, arelativcly high voltage is developed in the secondary winding of thetransformer; and when switch 6 is closed, a relatively low voltage isdeveloped in the secondary windlows lowered to touch the metal, and thensli htly withdrawn, so that an arc is forme be- Owing to the: relativelyhigh voltage applied to the electrode, the are is a long one. When themetal is melted, the switch 6 is opened and then the switch 2 is closed.The electrode is again lowered until the current begins to in .4 T carryout my improved process as fol-- Switch c 18 closed,and the electrode isflow; As the voltage applied to the electrode is now lower, the arebetween the electrode andvthe slag, which at this stage is floating onthe metal, willibe shorter. From this time, lintil the metal is poured,the supply of heat to the furnace, which of course is the electricpower, is adjusted in accordance with the requirements, bysmall-variations inthe position of .t lG BlBCt-I'OClG. Rais ing theelectrode decreasesthe current and vice versa. It is important to notethat the required movements of the electrode will be small. sun-e thevoltage'remains substanlially constant; and therefore the effect of anyalteration of the current, due to an adjustnient of the electrode. isnot neutralized by a substantial alteration. in the reverse direction,of the voltage. lheretore no substantialalteration in thelength of thearc is necessary when varying the power supply.

I claim as my invention: '1. The process of melting and refiningsteelior other metals which consists in forming an electric are betweena furnace electrode and the metal to melt the latter; subsequentlyforming between said electrode signature. c

QSEPH- LAWTON DIXON.

